Temperature compensated frequency stabilized composite dielectric resonator

ABSTRACT

A composite dielectric resonator having stabilized resonant frequency against the variation of ambient temperature, comprising two kinds of low attenuation dielectric elements each having the temperature coefficient of the dielectric constant in opposite signs. The two dielectric elements are coupled together so that the contact surface is extending substantially parallel to the vector direction of the high frequency electric field. Further improvement of the resonator for obtaining fine adjustment facility is achieved by providing at least an adjustable element, such as a metal post closely arranged to the resonator element for adjusting the electromagnetic energy in the resonator.

United States Patent [191 Konishi et al.

[ Mar. 19, 1974 1 1 TEMPERATURE COMPENSATED FREQUENCY STABILIZED COMPOSITE DIELECTRIC RESONATOR [75] Inventors: Yoshihiro Konishi, Sagamihara; Norio Hoshino; Yosuke Takano, both of Tokyo, all of Japan [30] Foreign Application Priority Data NOV. 26, 1970 Japan ..l 45%03634 [52] US. Cl 333/83 T, 333/83 R [51 Int. Cl. H01p 1/30, I-IOlp 7/00 [58] Field of Search 333/82 BT, 83 T, 83 R, 333/73 W, 73 S, 82 R; 331/176 [56] 9 References Cited UNITED STATES PATENTS 2,432,093 12/1947 Fox 333/83 R X 2.852.682 9/1958 Icenbice 333/8 2 BT 2.890.422 6/1959 Schlicke 333/33 R X 3.353.122 11/1967 Manoochehri. 333/73 W 3,504,303 3/1970 Konishi 333/83 T 3.613.035 10/1971 Askew 333/73 S 3,617,955 ll/l97l Masland 333/84 M 3,633,104 l/l972 Gray et a1. 333/83 T OTHER PUBLICATIONS Harrison, W. l-I., A Miniature High-Q Bandpass Filter Employing Dielectric Resonators MIT-l6, 4-l968,'pg. 210-218. Stiglitz, M. R., "Frequency Tuning of Rutile Resonators." Proc. IEEE, 3-1966, pp. 413-414. Vedam et al., Piezo-Thero-Optic Behavior of UN- b03" App. Physics Letters. Vol. 12, 2-1968, pp. 138-140. Clar, P., The Application of Dielectric Resonators to Microwave Integrated Circuits, Conf. Digest of Tech. Papers of the G-MTT 1970, Intern. Microwave Sym.

Newport Beach Calif. USA. 11-14 May 1970, pp. 19-23.

Bady et al., Dielectric Constant & Loss Tangent of Microwave Ferrites at Elevated Temperatures" M'IT-l 1, 7-1963, pp. 222-226..

Cohn, S. B.Microwave Bandpass Filters Containing High-Q Dielectric Resonators, M'l'T-l 6, 4-1968. pp. 218-227.

Gerdine, M. A. A Frequency-Stabilized Microwave Band Rejection Filter Using High Dielectric Constant Resonators MTT-l7, 7-1969, pp. 354-359. Day, Jr., W. R. Dielectric Resonators as Microstrip Circuit Elements, Conf. Digest of Tech. Papers of the G-M'IT 1970 Intern. Microwave Sym. Newport Beach Calif. USA. ll-l4 May 1970, pp. 24-28.

Stiglitz et al., Frequency Stability in Dielectric Resonators Proc. IEEE 3-1965, pp. 311-312.

Meagher et al., Practical Analysis of Ultra High Frequency RCA Service Co. Inc., 1943, pp. 18-19. Soohoo, R. F. Theory & Application of Ferrites Prentice-Hall Inc., 1960 pp. 142-143.

Primary Examiner-James W. Lawrence Assistant Examiner-Wm. I-I. Punter Attorney, Agent, or Firm-Stevens, Davis, Miller & Mosher [5 7] ABSTRACT A composite dielectric resonator having stabilized resonant frequency against the variation of ambient temperature, comprising two kinds of low attenuation dielectric elements each having the temperature coefficient of the dielectric constant in opposite signs. The

two dielectric elements are coupled together so that v the contact surface is extending substantially parallel 14 Claims, 31 Drawing Figures minimum m4 $198578 SHEEI 3 0f Temperafure 3 PATENTEDHAR 19 m4 SHEET 5 0F 9 WegaI/ve Tismperarare grad/en! Pas/rive Tmperafure grad/enf PMENTEBHAMS I915 3798.578

sum 9 or 9 TEMPERATITRE COMPENSATED FREQUENCY STABILIZED COMPOSITE DIELECTRIC RESONATOR BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a composite type dielectric resonator used in high frequency and more especially in millimeter wave range for which a stringent requirement for the stability of characteristics against temperature variation is imposed.

2. Description of the Prior Art For the miniaturization of the broadcasting equipment by introducing integrated circuit elements in quasi-millimeter wave range and for obtaining a high Q value in the filters, a small dielectric resonator made of an integrated circuit element applied with dielectric material by vaporization has been noticed. However, a practical dielectric resonator has not been realized mainly due to the temperature characteristics. The resonant frequency of such dielectric resonator shifts according to temperature variation and thus a practical device can hardly-be obtained.

M. R. Stiglitz J. C. Sethares had proposed a solution in Frequency Stability in Dielectric Resonator proceedings of the IEEE, Correspondence, March, 1965, page 311.

In the Stiglitz dielectric resonator, a dielectric resonator element is supported on an inner surface of a wave guide with aninterposition of a high frequency insulator having high thermal conductivity, such as boron nitride BN, so that the heat loss caused by high frequency power and produced in the dielectric element of the resonator, such as titanium oxide TiOz, is

dissipated to the surface of the wave guide.

By applying the above teaching in a dielectric resonator, temperature characteristics of resonant frequency can be improved as seen in FIG. 1, in which a curve I shows a temperature characteristics of the above Stiglitz dielectric resonator and a curve II shows that of an ordinary resonator without applying the high frequency insulator. In such Stiglitz dielectric resonator, however, it is impossible to eliminate an influence of the ambient temperature.

Another attempt is described in an article written by M;A. Gerdine entitled A Frequency Stabilized Microwave Band Rejection Filter Using Dielectric Resonators IEEE MTT-17 No. 7, July, 1969. FIG. 2 shows an embodiment of a dielectric resonator of this type, which comprises two dielectric elements, for example, disks of TiOQI and 3 oppositely arranged with an interposition of an air layer 5. The TiO disks 1 and 3 are supported respectively by rods 7 and-9 which are made of insulating material having high coefficient of thermal expansion and of low dielectric constant. These insulating rods 7 and 9 are fastened to the side walls 11 and 13 of a waveguide by means of clamps l5 and 17, respectively. In this embodiment, the interval between the dielectric elements 1 and 3 is varied according to the change of the length of each of the supporting insulators 7 and 9 which support the dielectric elements 1 and 3, respectively,- and the change of capacitance caused by the variation of said interval is utilized so as to compensate possible variation of resonant frequency characteristics owing to change of temperature of the dielectric elements. This principle can be applicable in designing a band rejection filter so as to stabilize frequency of the filter against temperature variation. However, this principle is not suitable for a band-pass filter, and has a drawback in that the frequency is easily varied by mechanical oscillation. Furthermore, it is difficult to realize fine adjustment mechanism for the resonant frequency while maintaining the resonant frequency compensation characteristics against temperature.

SUMMARY OF THE INVENTION The present invention has for its object to realize a dielectric resonator suitable for use in quasi-millimeter wave range and having stabilized frequency characteristics at varying ambient temperature.

The dielectric resonator according to the present invention is made in a composite type and comprising two kinds of low attenuation dielectric elements each having the temperature coefficient of the dielectric constant in opposite sign and the two elements are coupled in a manner that the contact surface is extending substantially parallel to the vector direction of the high frequency electric field.

More precisely, the two dielectric elements should be chosen in the following relationship. Assuming the tensor dielectric constants for the two dielectric elements are Ffand s? respectively, and the temperature coefficients of the constants; i.e.,

be a? J1 it at and at are in the following relationship:

wherein r; and 1- designate each dielectric region and E designates the vector component of the high frequency electric field.

Also the vector component of the high frequency electric field at the constant surface of the two elements is so arranged as to extend substantially parallel to the contact surface so that an influence of an air layer may be eliminated.

The present invention has its further object to provide a fine adjusting facility for such a composite dielectric resonator by providing at least an adjustable element, such as a metal post closely arranged to the resonator element, for adjusting the electromagnetic field energy trapped outside of the dielectric element as an evanescent mode.

In one aspect the invention provides a composite dielectric resonator comprising at least two different dielectric elements having temperature coefficients of relative dielectric constant in opposite sense, the dielectric elements are combined at a contact surface to form a resonator, wherein the oscillation mode in the resonator is selected to have high frequency electric field component extending parallel to said contact surface between the two dielectric elements.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a graph showing variation of resonant frequency owing to variation of temperature for two dielectric resonators;

FIG. 2 is a schematic cross-sectional view of a dielectric resonator of a known type proposed by Gerdine;

FIG. 3a is a perspective view of a cubic shaped dielectric resonator;

FIGS. 3b and 3c are the explanatory diagrams for the basic oscillation mode in the resonator shown in FIG. 3a;

FIG. 4a is a perspective view of a disk shaped dielectric resonator;

FIGS. 4b and 4c are diagrams showing the basic oscillation mode in the resonator shown in FIG. 4a;

FIG. 5a is a perspective view of a cylindrical shaped dielectric resonator;

FIGS. 5b, 5c and 5d are the diagrams showing the basic oscillation mode in the three sections of the resonator shown in FIG. 5a;

FIG. 6a is a perspective view of an embodiment of a composite dielectric resonator made in accordance with the present invention;

FIG. 6b is a perspective view of a different embodiment of a composite dielectric resonator according to the present invention;

FIG. 7 is a perspective view of a further embodiment of a dielectric resonator of the present invention;

FIG. 8 also a perspective view of another embodiment of a dielectric resonator of the present invention;

FIGS. 9 and 11 are graphs showing temperaturerelative dielectric constant characteristics of the dielectric materials used in the resonator of the present invention;

FIG. is a diagram illustrating condition of the contact surface between the two dielectric elements;

FIGS. 12a and 12b are explanatory diagrams for a composite dielectric resonator;

FIG. 13 is a cross-sectional view of a dielectric resonator made in accordance with the present invention showing the fine adjustment mechanism;

FIG. 14 is an explanatory diagram showing another embodiment for the fine adjustment;

FIG. 15 is a cross-sectional view of a practical embodiment of a composite dielectric resonator made in accordance with the present invention;

FIG. 16 is an equivalent electric circuit diagram of the resonator shown in FIG. 15;

FIG. 17 is a graph showing temperature adjustment characteristics of a resonator according to the present invention;

FIG. 18 is a graph showing a temperature-frequency characteristics of the resonator shown in FIG. 13 in comparison with that of a resonator of the conventional single type;

FIG. 19 is a temperature-frequency characteristics of the resonator shown in FIG. 15;

FIG. 20 is a cross-sectional view of a wave guide provided with a resonator according to the present invention;

FIG. 21 is a cross-sectional view of a band-pass filter using a dielectric resonator made in accordance with the present invention; and

FIG. 22 is a plan view of the band-pass filter shown in FIG. 21.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Before explaining full detail of the resonator according to the present invention, at first the basic oscillation modes in dielectric resonator of various forms will be explained.

There are three basic forms for the element of a dielectric resonator. These forms are rectangular form (a and b c), a disk form (L D) and a cylindrical form (L D) as shown in FIGS. 3a, 4a and 5a, respectively. The fundamental oscillation mode in a rectangular resonator as shown in FIG. 3a is the TE or dipole mode as shown schematically in FIGS. 3b and 3c. The fundamental oscillation mode in a disk resonator as shown in FIG. 4a is the TE mode as shown in FIGS. 4b and 4c in which the high frequency electric field E is extending parallel to the disk surfaces. The fundamental oscillation mode in a cylindrical resonator as shown in FIG. 5a is EI-I mode and the three sectional views of this EH mode are shown in FIGS. 5b, 5c and 5d. In this oscillation mode, a high frequency magnetic field H has magnetic dipole in a plane normal to the direction of the axis of the cylinder, and a high frequency electric field E is extending substantially parallel to the direction of the axis.

FIGS. 6a and 6b show schematically two basic principles of the dielectric resonator made in accordance with the present invention. The composite dielectric resonator shown in FIG. 6a is made of two stacked dielectric plates 21 and 23. The dielectric constant e, of the plate 21 and that of E of the plate 23 are chosen to have temperature coefficients in opposite polarities. In order to give such characteristics, the two plates are made of, for example, TiO and LiNbO respectively. The composite dielectric resonator shown in FIG. 6b is also made of two stacked dielectric plates 25 and 27 of which dielectric constants 6 and 6 are chosen to have temperature coefficients of opposite polarities.

As same as explained in the basic oscillation modes by referring to FIGS. 31), 3c, 4b and 4c, an electric field E in the oscillation mode in the embodiments shown in FIGS. 6a and 6b appear in parallel to the fiat contact plane between the two elements in both the rectangular shaped and disk shaped resonators.

FIG. 9 shows a graph illustrating curves of relative dielectric constants e l and e of e; for TiO against temperature. In the graph a curve denoted 6 depicts the variation of relative dielectric constant in a direction parallel to the optical axis of the dielectric material and e j is that in a direction normal to the optical axis.

FIG. 11 shows a corresponding graph for the relative dielectric constant for LiNbO As shown in the drawings, the and 6 have opposite sign in the temperature coefficient.

The disk resonator as shown in FIG. 4a can also be used in a composite dielectric resonator according to the present invention in a different form. In this embodiment the form may be altered as shown in FIG. 7 and a circular hole is bored at the center of a dielectric disk 29 having its relative dielectric constant e so as to insert an inner disk 31 having its relative dielectric constant e; which has temperature coefficient of opposite sign with e,. In this embodiment shown in FIG. 7, the electric field component becomes weaker at a location closer to the center of the disk 31, so that it is preferable to make the dielectric constant e; of the inserted inner disk 31 larger than. that of the dielectric constant 6 of the outer disk 29.

In case if the principle of the cylindrical resonator as shown in FIG. 5a is to be utilized, the electric field E appears substantially parallel to the direction of the axis of the cylinder. Therefore, a composite dielectric resonator according to the invention can be made of a hollow cylinder 33 having the dielectric constant and of an inserted dielectric rod 35 having the dielectric constant e; as shown in FIG. 8. The rod 35 is inserted into the hollow part of said cylinder 33. The temperature coefficients of the two dielectric constants 6 and 6 are selected to be opposite signs.

The use of the composite type resonator using the principle as shown in FIG. 8 is limited to the basic oscillation mode and EH mode in which the electric field is extending substantially parallel to the axis of the cylinder.

When higher oscillation mode I-IE is produced in addition to said fundamental mode, the electric field component of the higher oscillation mode HE lies substantially parallel to a plane normal to the direction of the axis, and an electric field vector of the higher mode has radial component B which is directed toward the radial direction of the cylinders 33 and 35. As a result, if the contact surface of the two dielectric elements lies in the direction of axis as shown in the structure of FIG. 8, the electric vector near the contact surface is extending normal to the contact surface as shown in FIG. 10. For such oscillation mode the embodiment as shown in FIG. 8 is not suitable.

Because in such case, as the higher frequency electric field component E is intersecting normal to the contact surface, it is necessary to make the contact surface of both dielectric elements to be an optical contact plane by a reason set forth below.

Assuming, for example, that an air layer 37 is formed as shown in FIG. 10 owing to possible loose mechanical contact between the dielectric elements 39 and 41, a strong electric field is applied onto the air layer. If we assume the relative dielectric constant of the dielectric element as 6,, and the electric field in the element as E, the electric field strength in the air layer 37 is e E. Thus, the electric energy density in the air layer 37 is 6, times larger than that in the dielectric element. Hence, the effect of the electric energy in the air layer 37 having thickness 1,, upon the deviation of the resonant frequency is substantially proportional to E r and is also substantially overall proportional to Erta/D, considering the diameter D of the dielectric element. When the frequency deviation is desired to be limited below p X 10", (p is a constant value and x isan index) and the thickness t of the air layer 37 must fulfil a condition expressed as follows:

If the relative position between both the dielectric elements is varied in order to perform the desired frequency compensation for the temperature variation or by a reason of secular deviation, said thickness t of the contact plane cannot always be a constant value so that a certain deviation in amount of Ar occurs. In this situation, it is desired to make the frequency deviation caused by said deviation Ar to be smaller than an influence caused by temperature variation. In order to finally limit the frequency variation in a desired amount p X 10" at a' certain range of temperature variation, said deviation of the thickness t,,+A't, must be maintained in an extent shown in the equation (2). In case of using TiO having characteristics as shown in FIG. 9 as the dielectric element, the relative dielectric constant e, is about 70 100. The diameter D of the dielectric disk is to be made in an order of about 5 mm in the frequency band of quasi-millimeter wave. If the frequency deviation due to temperature variation is desired to be finally limited within an order of 10 (p =l,x=4) by the dielectric compensation, the amount t -l-A t must satisfy: t -l-At E 0.0005 p. which is derived from the above equation (2). If Al /t nearly equals 0.1, then t,, 0.0005 ;1. is obtained. Above explanation is concerned for the adjustment for frequency compensation against temperature, but this principle can also be applied to the adjustment of the resonant frequency. In this application, if a fine adjustment range of the frequency is desired to be within p 10", the amount of At,, must be limited to a value determined by said expression (2). Now, it should be noted that the thickness t,, of said air layer 37 in FIG. 10 must be less than 0.005 micron, in case of applying the structure of FIG. 8 to said HE mode. It is, however, nearly impossible to obtain such an air layer of 0.005 micron, which is an optical contact surface, in view of accuracy of machining.

In the oscillation mode of ll-IE, in the embodiment shown in FIG. 6b, the electric field component E is always parallel to the contact surface between the two v elements. Consequently, if the contact surface of said two dielectric elements is arranged as shown in FIG. 6b to extend parallel to the direction of the electric field, then said thickness t of the air layer 37 may be allowed up to 6,- times, i.e., up to an order of 0.5 micron. This means that the machining accuracy is allowed for times less. Usually such accuracy can easily be satisfied.

Furthermore, in order to obtain more perfect frequency compensation against temperature variation of the dielectric resonator, the dielectric disk is formed in such a way that an optical or crystal axis is included in a surface of the disk 25 or 27 as shown in FIG. 6b. Generally, a dielectric element has different dielectric constant in different direction, i.e., a value 6 in the direction of the crystal axis and a value 6 i in the direction of the surface which is normal to said axis differ each other. In case of TiO and LiNbO for example, they have such temperature characteristics as shown in FIGS. 9 and 11, in which generally it applies 6 3L e,,.

Accordingly, if both dielectric disks 43 and 45, each of which is a component of the composite dielectric according to this invention, are so arranged that directions of optical axes of these disks are parallel to one another, as depicted by arrows shown in FIG. 12a, and also if this composite dielectric is operated in the oscillation mode of HE then the electric field in thecross section which is normal to the axis of the cylinder of each dielectric 43 and 45 is mainly directed to the direction of i.e., to the direction normal to the optical axis. On the contrary, if both dielectric disks 43 and 45 are arranged in a manner that their optical axes cross normal to each other, as depicted by arrows shown in FIG. 12b, the direction of electric field in the direction of an intermediate angle between two optical axes is not always coincident with the direction of the intermediate angle, but is directed rather closer to a direction normal to the optical axis of the dielectric element, the e i value of which is larger than that of the other dielectric element of said two dielectric elements which compose a composite dielectric.

Thus, the degree of contribution of a dielectric constant of each dielectric to electric energy can be varied by changing the intersecting angle formed by the two axes of said both dielectric elements. According to the present invention, two dielectric elements having the dielectric constants each of which varies in the opposite sense by the change of temperature are combined so as to change the intersecting angle of two axes of the component dielectric element, so that it is possible to make frequency compensation against temperature variation by adjusting said angle of two axes in order to satisfy said equation (1). In this case, however, it follows that the resonant frequency is forced to vary by the above adjustment, therefore, it is necessary to separately provided a means for adjusting finely the resonant frequency. For example, in a composite dielectric resonator according to this invention, which is shown in FIG. 13, dielectric disks 47 and 49 are mounted on an earth plate 51 by a supporting bed 53 of insulating material having a small dielectric constant, at the center of which bed 53 a cavity 55 is provided. A member 56 for varying the resonant frequency, such as a screw of metal or dielectric substance is adjustably fitted so as to finely tune the resonant frequency by varying the length of a portion of said screw 56 which enters into said cavity 55.

FIG. 14 shows another embodiment made in accordance with the present invention, in which a composite dielectric resonator comprises a 'TiO disk 57, a LiNbO disk 59 and a thin disk 61 made of either one of the dielectric materials TiO and LiNbO which third disk 61 is placed on the stacked disks 57 and 59. By rotating said disk 61 about the axis, the resonant frequency may be varied finely. In this embodiment, the direction of the electric field in the thin disk 61 depends mainly upon the electrical field in the two thick disk 57 and 59, as described above. Since in case of using HE mode, the direction of electric field in the section parallel to each axis of the disks 57 and 59 is hardly influenced by the direction of the axis of the thin disk 61, if the axis of the thin disk 61 is coincident with the axis of the thicker disk 59 thereunder, equivalent dielectric constant of the thin disk 61 is nearly c whereas if the axis of said disk 61 is normal to the axis of said disk 59, the equivalent dielectric constant in said disk 61 is nearly equal to e As a result of this, if a dielectric material which satisfies the relation 6 e is used as a dielectric material of the thicker disk 59, then the resonant frequency takes a minimum value when the direction of the axis of the thinner disk 61 is coincident with that of the thicker disk 59, and resonant frequency takes a maximum value when both directions of these axes are normal to each other. That is .to say, resonant frequencyof the composite dielectric can be finely adjusted by rotating said thinner disk 61.

In accordance with the present invention, as described above, variation of resonant frequency caused by variation of temperature can be cancelled by combining two different kinds of dielectric materials, dielectric constants of which have opposite signs to one another, so thatit is possible to provide a composite dielectric resonator having highly stabilized resonant frequency. Moreover, since a dielectric resonator according to this invention is so arranged that the high frequency electric field does not cross normal to the air layer at the contact part of both dielectric elements, the resonant frequency is not shifted in spite of the change of said air layer, even if a condition of said air layer may be changed by a lapse of time or by a mechanical oscillation. On the contrary, according to the dielectric resonator of Gerdine, the dielectric compensation is performed by the change of capactance between two dielectric elements, so that the resonant frequency is shifted by the change of the gap between two dielectric elements. Furthermore, a remarkable effect is obtained that frequency compensation against temperature and fine adjustment of frequency can easily be realized by varying relative locations of both the dielectric elements in the contact plane thereof.

In a practical form of the resonator made in accordance with the present invention, further fine adjustment mechanism is provided for adjusting compensation characteristics of frequency deviation due to temperature variation. The basic fonn of resonator as explained above has a contact surface between two basic dielectric elements. Outside of the resonator or more precisely outside of both other surfaces of the composite dielectric resonator, an oscillation mode is produced which is termed as an evanescent mode. In this evanescent mode region, if we consider, for instance, TE mode, the magnetic energy is much stronger than the electric energy of the oscillation mode. The present invention has been attained by the recognition of the above fact.

In accordance with the present invention, at least an adjustable metal element is provided in the evanescent mode region outside of the resonator to adjust the interval between the metal element and the resonator surface so that the magnetic energy in a dielectric element is adjusted to control its contribution rate for the resonant oscillation of the resonator and a fine adjustment of the frequency deviation clue to temperature variation is obtained.

In the above embodiment according to the present invention shown in FIG. 13, frequency deviation up to a few MHz in 10 GI-Iz band at a temperature variation range of 20C to +C can be compensated. However, by applying only the basic principle of said embodiment of the invention, it has been difficult to compensate the frequency deviation more finely, i.e., in order of less than 1 MHz.

FIG. 15 shows a more practical and preferred embodiment of the present invention, in which a strip line transmission path 71 is arranged between outer shielding plates 73 and 75 with interposition of supports 77 and 79 of insulating material having low dielectric constant, such as Teflon (Trade Name). A composite dielectric resonator made in accordance with the basic principle of this invention, which comprises flat disk or cubic shaped dielectric elements 81 and 83,- is disposed beside the strip line 71 and is supported on a supporting bed 85 having a cavity 85a. Tapped holes 87 and 89 are bored in the shielding plates 73 and 75 at positions opposite to said dielectric resonator comprising elements 81 and 83. Threaded metal posts 91 and 93 are screwed into said holes 87 and 89, respectively, so that the distance between each top surface of said posts 91 and 93 and respective dielectric elements 81 and 83 can be varied by moving said metal posts 91 and 93 in the direction as illustrated by arrows in the drawing. It is to be noted that the thickness of the bottom of said cavity 85a bounded by the support bed 85 should be made sufficient dimension for supporting said dielectric elements 81 and 83, and also it must be arranged not to obstruct the screwing of said metal post 93.

FIG. 16 shows an equivalent electrical circuit of the embodiment shown in FIG. 15. An upper-side impedance Z viewed from the dielectric element 81 having characteristic impedance Z' for the upper side, i.e.,

air side, is inductive in case of TE, oscillation mode.

The inductive component of the impedance Z becomes lower as the post 91 is moved closer to said dielectric element 81. Accordingly, the impedance Z, viewed from said dielectric element 81 into the upper evanescent region assumes smaller value, and accordingly as the post 91 is moved closer to the dielectric elemerit 81, the magnetic energy in said dielectric element 81 increases. same effect is applied to the lower side impedance Z viewed from the dielectric element 83 having characteristic impedance 2 into lower-side, i.e., air side.

Qti the o therhand, the strength E of the electric field in the circumferential direction in the dielectric element is always in a particiilar relation with the strength l-l of the magnetic field in'the axial direction in the dielectric element. Since the total energy in the dielectric resonator is constant and this energy is distributed both to magnetic and electric energies, the electric field strength E in the-resonator decreases according to an increase of the magnetic field therein, therefore the electric field energy in said two dielectric elements concentrates inside of the dielectric element apart from the metal posts 91 and 93.

If the dielectric materials the respective relative dielectric constant of which increases or decreases in response to temperature rise, for example, TiO and LiNbO are used as the material of the dielectric elemerits 81 and 83, respectively, the ene'rgy distribution to magnetic and electric energies in both dielectric elethe composite dielectric resonator can be adjusted to be either negative or positive sense.

In order to maintain the resonant frequency to be constant under a certain temperature, the post 93 should be so adjusted to move away from the dielectric element 83 when the post 91 is moved toward the dielectric element 81 and vice versa. The former adjustment is effective to make the temperature gradient of resonant frequency to be negative and the latter adjustment is efficient to make the gradient positive.

FIG. 17 shows characteristic curves for various combination of the distance between-the respective post and the respective dielectric element, when the resonant frequency is adjusted to be constant. The distance h between the dielectric element 81 and the post 91 and the distance h, between the dielectric element 83 and the post 93 are expressed by a ratio with a diameter 2a of said dielectric elements 81 and 83. In F lG. 17, the absicissa and the ordinate are scaled by value h /2a and h /Za, respectively. This graph shows curves for a constant frequency for various combinations of these valties. In this figure, parameter Xo shown at each curve is obtained by multiplying propagation constant in free space by the radius a of the dielectric element. A locus merits 81 and 83 varies, i.e., the magnetic energy in the dielectric element 81, i.e., in TiO relatively increases and the electric energy in the same dielectric element 81 relatively decreases, and the magnetic energy in the dielectric element 83, i.e., in LiNbO relatively de-' creases and the electric energy in. the same dielectric element 83 relatively increases when the metal post 91 is moved toward the dielectric element 81. This is equivalent to a case when we assume the electric field intensity of the dielectric element 81 made of TiO becomes lower. 1

As a result, the contribution to the resonant frequency by the dielectric element 81 the electric field strength of which is lower decreases, and thus the fre quency variation caused by the temperature rise of the resonator shifts toward lower frequency when the temperature increases. Namely, the temperature gradient of the resonant frequency is negative in this adjustment. Conversely, if the metal post 93 is moved toward the dielectric element 83, the magnetic energy in said element 83 tends to increase and the contribution of said element 83 to the resonant frequency decreases, so that when LiNbO having relative dielectric constant which increases according to temperature rise, is used as the other dielectric element 83, as in the case of this embodiment, frequency deviation due to temperature rise of the resonator shifts toward higher frequency when temperature increases. Thus, the temperature' gradient of the resonant frequency is positive in this adjustment. i

In summary, according to the adjustment Whether the post 91 is moved toward the dielectric element 81 or the post 93 is moved toward the dielectric element 83, the temperature gradient of the resonant frequency of P which indicates the temperature gradient being zero at the resonant frequency is dipicted by connecting the center points of the curves. The temperature gradient of the resonant frequency assumes negative value when the distance values h /2a and 11 /211 are located in a region above said locus P marked as negative and the gradient assumes positive value when both values are located in a region below said locus P marked as positive."

In accordance with the present invention, as de- I scribed above, the distance between the metal post and the dielectric element is so adjusted that the deviation of resonant frequency due to temperature variation owing to the variation of the temperature characteristics of thedielectric elements, can be compensated.

The experimental result of the compensation according to the present invention is now compared with the case of the prior art dielectric resonator. The result is shown in FIG. 18. In this figure, a dotted curve I shows a temperature characteristics of a single type known dielectric resonator employing only TiO whereas a solid curve II shows that of a composite dielectric resonator as shown in FIG. l3.according to this invention. Comparing these curves I and II, it is clearly distinguished that shift of resonant frequency against temperature variation in the composite dielectric resonator is much less than that in the single dielectricresonator. Furthermore, it is found that when using the composite dielectric resonator shown in FIG. 15, shift of the resonant frequency is limited within 200 KHz in the temperature range of -20C to +C at a frequency band of 10 GHz, by appropriately adjusting both of the metal posts 91 and 93, the curve of the temperature characteristics of this embodiment is illustrated in FIG. 19.

FIG. 20 shows an embodiment of applying this invention in a waveguide. In FIG. 20, a composite dielectric resonator is composed of two dielectric elements 101 and 103 having flat cylindrical or cubic shape having the axis normal to the side surfaces (E surfaces) 105 and 107 of the waveguide. This resonator formed by two elements 101 and 103 is supported to the bottom surface (l-l surface) 109 of this waveguide by supporting a base 111 made of ceramics as an insulating material having low relative dielectric constant. In positions where the axes of said dielectric elements 101 and 103 are crossed with the E surfaces 105 and 107, metal posts 113 and 115 are adjustably arranged to change the distance between said dielectric elements 101 and 103 and said posts 113 and 115, respectively.

The above mentioned embodiments of the invention are directed to band rejection filters. On the other hand, in order to provide a band-pass filter by using a strip transmission line, a composite dielectric resonator according to this invention may be arranged in the manner as shown in FIGS. 21 and 22. Referring now to FIGS. 21 and 22, a composite dielectric resonator composed of two dielecric elements 121 and 123 are disposed in a coupling area of two strip lines 125 and 127, each end portion of which is short-circuited to the ground and which are positioned between two shielding plates 129 and 131 by means of a supporting bed 133 made of insulating material having low relative dielectric constant. Said supporting bed 133 is provided with a cavity 135 with a thin partition 137 between said dielectric element 123 and said cavity 135. The shielding plates 129 and 131 are bored with screw holes 139 and 141, respectively, in parts where these shielding plates 129 and 131 are opposed to said dielectric elements 121 and 123, respectively. Threaded metal posts 143 and 145 are screwed into said holes 139 and 141, respectively, so that these posts 143 and 145 are screwed into said shielding plates 129 and 131 toward said dielectric elements 121 and 123.

In case of providing a band-pass type filter by using a waveguide, a composite dielectric resonator of the type shown in FIG. 20 is positioned within a cut-off waveguide, to which input and output circuits are coupled.

In accordance with the improved aspect of the present invention, a fine adjustment of the temperature compensation of the resonant frequency can also be realized by varying the distance between the metal posts and the dielectric elements, and which provides very easy adjusting facility. When TE mode is applied to the composite dielectric resonator according to this invention, an induced current on the shielding plate flows in the circular direction of the metal post, so that there is no conductor loss due to the adjusting movement of the metal post. Accordingly, fine adjustment of the temperature compensation of resonant frequency can be realized without decreasing value.

Moreover, the present invention has an advantageous effect of being able to adjust the temperature gradient of the resonant frequency as well as resonant frequency itself. That is to say, it is possible to adjust temperature gradient equal to zero at a given frequency.

Although some embodiments of the present invention have been described, the present invention is not limited to the particular embodiments and many modifications and alterations are possible without departing from the scope of the present invention.

We claim:

1. A composite dielectric resonator, comprising first and second dielectric elements, the direction of change, with respect to frequency, of the temperature coefficient of the relative dielectric constant of said first element being opposite to that of said second element, said dielectric elements being made of stacked rectangular shaped elements combined to contact each other at respective surface portions to form said composite resonator, said resonator having an oscillation mode with a high frequency electric field component extending parallel to the contacting surface portions of said dielectric elements, said elements being chosen to have relative temperature coefficients which, in said composite resonator, provide a stabilized resonant frequency over a wide range of temperature variation of said resonator.

2. A composite dielectric resonator according to claim 1, further comprising a metal rod arranged closely in opposition to an outer surface of the resonator so as to adjust an interval between the metal rod and the resonator surface to control the magnetic field component in the dielectric elements.

3. A composite dielectric resonator as claimed in claim 1, wherein the dielectric materials are chosen to be TiO and LiNbO 4. A composite dielectric resonator as claimed in claim 1, wherein a pair of metal posts are adjustably arrangedopposite to the resonator surfaces to control the magnetic field component in the dielectric elements.

5. A composite dielectric resonator as claimed in claim 1, wherein said two metal posts are adjustably screwed in two shielding plates constituting outer container of the resonator.

6. A composite dielectric resonator according to claim 1, wherein the resonator is secured on a support attached on a shielding plate forming a part of an outer wall of a waveguide cavity, and a pair of metal rods are adjustably arranged to move in an axial direction at the shielding plate and another shielding plate opposite thereto in a manner that the distances between the top surfaces of the metal rods and the resonator surfaces can be adjusted.

7. A composite dielectric resonator as claimed in claim 6, wherein the two shielding plates are provided parallel to each other, each having said metal rod screwed therein allowing axial movement toward the resonator outer surfaces and a strip line transmission circuit arranged between said two shielding plates with an interposition of supporting elements made of low dielectric constant insulating material.

8. A composite dielectric resonator, comprising first and second dielectric elements, the direction of change, with respect to frequency, of the temperature coefficient of the relative dielectric constant of said first element being opposite to that of said second element, said dielectric elements being made of stacked flat disk-shaped elements combined to contact each other at respective surface portions to form said composite resonator, said resonator having an oscillation more with a high frequency electric field component extending parallel to the contacting surface portions of said dielectric elements, said elements being chosen to have relative temperature coefficients which, in said composite resonator, provide a stabilized resonant frequency over a wide range of temperature variation of said resonator.

9. A composite dielectric resonator according to claim 8, further comprising a metal 'rod arranged closely in opposition to an outer surface of the resonator so as to adjust an interval between the metal rod and the resonator surface to control the magnetic field component in the dielectric elements.

10. A composite dielectric resonator as claimed in claim 8, wherein the dielectric materials are chosen to be TiO and LiNbO 11. A composite dielectric resonator as claimed in claim 8, wherein a pair of metal posts are adjustably ar ranged opposite to the resonator surfaces to control the magnetic field component in the dielectric elements.

12. A composite dielectric resonator as claimed in claim 8, wherein said two metal posts are adjustably screwed in two shielding plates constituting outer container of the resonator.

13. A composite dielectric resonator according to claim 8, wherein the resonator is secured on a support attached on a shielding plate forming a part of an outer wall of a waveguide cavity, and a pair of metal rods are adjustably arranged to move in an axial direction at the electric constant insulating material, 

1. A composite dielectric resonator, comprising first and second dielectric elements, the direction of change, with respect to frequency, of the temperature coefficient of the relative dielectric constant of said first element being opposite to that of said second element, said dielectric elements being made of stacked rectangular shaped elements combined to contact each other at respective surface portions to form said composite resonator, said resonator having an oscillation mode with a high frequency electric field component extending parallel to the contacting surface portions of said dielectric elements, said elements being chosen to have relative temperature coefficients which, in said composite resonator, provide a stabilized resonant frequency over a wide range of temperature variation of said resonator.
 2. A composite dielectric resonator according to claim 1, further comprising a metal rod arranged closely in opposition to an outer surface of the resonator so as to adjust an interval between the metal rod and the resonator surface to control the magnetic field component in the dielectric elements.
 3. A composite dielectric resonator as claimed in claim 1, wherein the dielectric materials are chosen to be TiO2 and LiNbO3.
 4. A composite dielectric resonator as claimed in claim 1, wherein a pair of metal posts are adjustably arranged opposite to the resonator surfaces to control the magnetic field component in the dielectric elements.
 5. A composite dielectric resonator as claimed in claim 1, wherein said two metal posts are adjustably screwed in two shielding plates constituting outer container of the resonator.
 6. A composite dielectric resonator according to claim 1, wherein the resonator is secured on a support attached on a shielding plate forming a part of an outer wall of a waveguide cavity, and a pair of metal rOds are adjustably arranged to move in an axial direction at the shielding plate and another shielding plate opposite thereto in a manner that the distances between the top surfaces of the metal rods and the resonator surfaces can be adjusted.
 7. A composite dielectric resonator as claimed in claim 6, wherein the two shielding plates are provided parallel to each other, each having said metal rod screwed therein allowing axial movement toward the resonator outer surfaces and a strip line transmission circuit arranged between said two shielding plates with an interposition of supporting elements made of low dielectric constant insulating material.
 8. A composite dielectric resonator, comprising first and second dielectric elements, the direction of change, with respect to frequency, of the temperature coefficient of the relative dielectric constant of said first element being opposite to that of said second element, said dielectric elements being made of stacked flat disk-shaped elements combined to contact each other at respective surface portions to form said composite resonator, said resonator having an oscillation more with a high frequency electric field component extending parallel to the contacting surface portions of said dielectric elements, said elements being chosen to have relative temperature coefficients which, in said composite resonator, provide a stabilized resonant frequency over a wide range of temperature variation of said resonator.
 9. A composite dielectric resonator according to claim 8, further comprising a metal rod arranged closely in opposition to an outer surface of the resonator so as to adjust an interval between the metal rod and the resonator surface to control the magnetic field component in the dielectric elements.
 10. A composite dielectric resonator as claimed in claim 8, wherein the dielectric materials are chosen to be TiO2 and LiNbO3.
 11. A composite dielectric resonator as claimed in claim 8, wherein a pair of metal posts are adjustably arranged opposite to the resonator surfaces to control the magnetic field component in the dielectric elements.
 12. A composite dielectric resonator as claimed in claim 8, wherein said two metal posts are adjustably screwed in two shielding plates constituting outer container of the resonator.
 13. A composite dielectric resonator according to claim 8, wherein the resonator is secured on a support attached on a shielding plate forming a part of an outer wall of a waveguide cavity, and a pair of metal rods are adjustably arranged to move in an axial direction at the shielding plate and another shielding plate opposite thereto in a manner that the distances between the top surfaces of the metal rods and the resonator surfaces can be adjusted.
 14. A composite dielectric resonator as claimed in claim 13, wherein the two shielding plates are provided parallel to each other, each having said metal rod screwed therein allowing axial movement toward the resonator outer surfaces and a strip line transmission circuit arranged between said two shielding plates with an interposition of supporting elements made of low dielectric constant insulating material. 